The primary long term goal of this research is to develop methods for studying mechanisms of protein association-dissociation reactions. Secondarily, I intend to examine one of the enzymes responsible for glutamate metabolism in the brain in order to determine what factors regulate it. In one of the most common enzyme control mechanisms, changes in activity follow changes in the association state of the enzyme. The generally available techniques for studying this process provide information only about the equilibria involved; the actual mechanisms by which dissociation occurs remain unknown. I propose to study these mechanisms. As with enzyme reactions, dissociation mechanisms could be determined by examining the kinetics of the process. This is not ordinarily possible; protein usually do not undergo a chemical change when they dissociate. In arginine decarboxylase from Escherichia coli B, however, a single sulfhydryl per subunit becomes available when the decamer dissociates to the dimer. We have begun to develop an approach to the study of dissociation mechanisms which takes advantage of this change in reactivity; we follow arginine decarboxylase dissociation by reaction with 5,5'-dithiobis-(2-nitrobenzoic acid), using a stopped-flow spectrophotometer to obtain initial rates of dissociation. Once the dissociation mechanism of arginine decarboxylase has been established by chemical means, I plan to use this as a model system in order to develop light scattering techniques for determining dissociation mechanisms. Since light scattering can measure changes in the weight average molecular weight, we should then be able to apply the kinetic techniques developed with arginine decarboxylase to enzyme which do not give an apparent chemical change when they dissociate. Specifically, we intend to examine the dissociation mechanisms of glutaminase, a brain enzyme whose association state is affected by a number of small ions.